The worldwide trend of increased saturated fat and carbohydrate consumption with increased omega-6 (n-6) and decreased omega-3 (n-3) fatty acid intake has coincided with the growing prevalence of chronic, life-threatening diseases, suggesting a critical link between the shift in our dietary composition and today's health epidemic (Leaf and Weber (1987) Am. J. Clin. Nutr. 45: 1048-1053; Cordain, L. et al. (2005) Am. J. Clin. Nutr. 81: 341-354). Saturated fats can be readily produced from carbohydrates in mammals, and both saturated fats and carbohydrates are highly abundant in the modern Western diet (Institute of Medicine of the National Academies. Dietary fats: total fat and fatty acids. In: Dietary reference intakes for energy, carbohydrate, fiber, fat, fatty acids, cholesterol, protein, and amino acids (macronutrients). (2002) Washington, D.C.: The National Academy Press, pp. 335-432); in contrast, omega-3 fatty acids cannot be made de novo nor converted from other nutrients in mammals, and therefore must be obtained from dietary sources (e.g., fish oil). Id.
Normally, mammals readily obtain saturated fatty acids (SFA) from either the diet or endogenous synthesis from glucose or amino acids (Volpe and Vagelos (1976) Physiol. Rev. 56, 339-417), and monounsaturated fatty acids (MUFA) can also be obtained from the diet or converted from SFA by the stearoyl-CoA desaturase-1 (SCD-1) gene (Paton and Ntambi (2009) Am. J. Physiol. Endocrinol. Metab. 297: E28-37). On the other hand, n-6 and n-3 PUFA cannot be inter-converted or synthesized de novo in mammals and are mainly acquired through the diet (Leonard et al. (2004) Prog. Lipid Res. 43: 36-54; Gebauer et al. (2006) Am. J. Clin. Nutr. 83, 1526s-1535s). In this context, to increase the tissue content of essential fatty acids, they must be supplemented in the diet, such as adding vegetable oils (e.g., corn, soybean, safflower, etc.) for n-6 PUFA or fish oil for n-3 PUFA.
The high fat diet has been widely investigated for its role in the development of metabolic diseases (Kuller (1997) J. Am. Diet. Assoc. 97: S9-15; Joint WHO/FAO Expert Consultation. (2003) Diet, Nutrition and the Prevention of Chronic Diseases (WHO technical report series 916). World Health Organization, Geneva. pp. 81-94). However, the interpretation of results from these reports often does not recognize the different types of fats—including saturated fatty acids (SFA), monounsaturated fatty acids (MUFA), n-6 polyunsaturated fatty acids (PUFA), and n-3 PUFA—that can each contribute differential effects to study outcomes (Weisburger (1997) J. Am. Diet. Assoc. 97, S16-23; Simopoulos (2008) Exp. Biol. Med. 233, 674-688). In addition, comparative nutrition studies conventionally utilize diets with different fat sources, introducing other variables that can become confounding factors (Kang (2011) World. Rev. Nutr. Diet. 102: 22-29). For example, the presence of many other components, other than n-6 or n-3 fatty acids, in the supplemented oils makes it difficult to interpret the experimental outcome for the authentic effect of n-6 or n-3 fatty acids. By overlooking or failing to isolate the respective impact of specific fats, the existing research has often presented inconsistent or contradicting conclusions, causing confusion among scientists and the public alike. Accordingly, there is a need for a reliably defined source of essential fatty acid type and quantity, which can be used as food sources to supplement essential fatty acids or as an experimental model for study of conditions associated with fat metabolism.